Engine burner, such as those used in Stirling engines, have one or more heat exchangers that produce significant back pressure at the air and fuel injection points. This back pressure can exceed 0.5 pounds per square inch gauge (“PSIG”). Gaseous fuels in most buildings and homes are supplied at pressures well below 0.5 PSIG. A fuel pump in the gas supply train may be used to raise the fuel pressure high enough to allow efficient mixing with of fuel with air. Prior art engines include some type of valve or throttle plate or other restrictive device to meter fuel into a combustion chamber. This restrictive device adds to the parts count and complexity for these engines. Elimination of such restrictive devices would simplify engine design.